(1) Field of the Invention
The present invention relates to a vapor deposition area of an organic layer in an organic electroluminescence (EL) display device.
(2) Description of the Related Art
As methods for forming a film of an organic layer of an organic EL display device there are known a printing method and a vapor deposition method. It is mainly the vapor deposition method that is practically applied to an organic EL display device using a low molecular organic material. Also as to an upper electrode, a film is formed mainly by vapor deposition.
A laminate structure of a conventional organic film is composed of an anode electrode as a lower electrode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode electrode as a combined upper electrode and electron injection layer of LiF/Al.
In case of adopting a distinctive coating method which affords light emitting layers different pixel by pixel, it is also known to form the anode electrode, hole injection layer, hole transport layer and cathode electrode as a continuous film common to all pixels and effect coating distinctively pixel by pixel causing the electron transport layer and the light emitting layer to emit light.
The present inventor has been studying the structure of a bottom emission active matrix type organic EL display device. According to this structure now under study, the metal of a cathode serving as an upper electrode is formed as a film just above an organic film and, for the supply of voltage to the cathode, the cathode is connected through a bank contact hole to an electrode (cathode contact) provided on a circuit board wiring.
Heretofore, contact holes for cathode contacts have not been disposed near pixels because of a poor deposition accuracy using a vapor deposition mask. In the sense of preventing a lowering of cathode voltage it is preferable that the number of cathode contacts be as large as possible and be positioned near pixels. When the degree of design freedom is taken into account, it is preferable that the number of areas where cathode contacts can be disposed be as large as possible.
A conventional vapor deposition mask is poor in vapor deposition accuracy particularly at an opening end thereof and, when it is intended to form a uniform film including display pixels, it has heretofore been required to vapor-deposit an organic layer up to an area going largely over a display pixel area and a dummy pixel area.
It is an object of the present invention to provide an organic EL display device which is high vapor deposition accuracy even if the vapor deposition area located outside display pixels and dummy pixels is small and which can improve the degree of design freedom.